Electrically controlled hybrid superconductor–ferromagnet cell for high density cryogenic memory

We report the fabrication and testing, at 4.2 K, of an S₁IS₂FS₃ device, where S, F, and I denote a superconductor (Nb), a ferromagnetic material (Permalloy), and an insulator (AlO_x), respectively. The F layer covers about one half of the top electrode of the S₁IS₂ Josephson junction and is positioned off-center. Electric current, I_tr, along the S₃ electrode can change the magnetization of the F layer in such a way that, for one direction of I_tr, a magnetic flux penetrates the junction perpendicular to the layers, whereas for the opposite direction, the perpendicular magnetic flux can be removed. In the former state, the modulation pattern of the Josephson critical current, I_c, in the magnetic field, H, may acquire minimum near H = 0 and restores its usual shape with maximum in the second state. These states can be used for building a compact cryogenic memory compatible with single flux quantum electronics.